Judgement counts. We all make a lot of decisions in business and like to think that we make the big ones with enough time, care and attention that we can be reasonably certain that they are rational, consistent and safe.

But just how consistent and careful are we? How far are our decisions influenced by external trivia? That's the question three business school academics set out to answer when they studied decision making by parole judges.

The law was a good test bed; legal decisions are more rules-bound than in business and therefore (it might be assumed) less susceptible to wide variation. Deciding on a prisoner's parole is a palpably serious issue that warrants and gets serious, concerted attention, so you'd expect consistent decision making.

But what they found was shocking: It was more likely that a prisoner would be granted parole if the application was heard at the very beginning of the work day or after a food break.

The reasons for this are intriguing and important.

Energy consumption. Making any kind of choice—between buying a car, a dress, a house, or hiring an employee—depletes mental resources. That's one reason you get hungry and crave sugary foods: your brain quite literally wants energy in the form of glucose.

Inadvertent simplification. As your brain gets tired, it strives to conserve energy, and it does so by simplifying choices. We are more likely to accept the status quo when a decision is needed after many have already been made. Over time, we just reach for the simplest answer.

The good news is there are ways to enhance your decision making.

Eat breakfast. Your brain needs the calories and you make better decisions when your brain has the energy it needs.

Make decisions early in the day. Save the most important ones for first thing in the morning. Procrastinators won't like this but there's a vast body of evidence showing that morning is when you're freshest. 

Gauge your exhaustion. Pay attention to how tired you are. Many of us see fatigue as something to be powered through and we feel heroic when we work long days. But there's nothing smart about putting yourself in a position that you're likely to make poor decisions.

Take breaks. Working without pause can feel intense and satisfying but after a while, you will reach for increasingly simple solutions. If you tend to over-complexify problems, you might need to get tired—but otherwise, don't think it's weak to give yourself a break. You may feel efficient and powerful making a whole string of decisions in a single sitting—but it can also be stupid, and make you vulnerable to extraneous influences we scarcely perceive. 

Research shows that there are a few other ways to re-charge your cognitive batteries: look at scenes of nature, take a short nap, experience some kind of positive mood, or eat a meal. All these things can significantly recharge your mental batteries. Brain gym and other gimmicks won't help but cardio-vascular exercise will.

What I find especially intriguing about this research is that we tend to imagine human judgment is a fairly fixed characteristic. (Psychometric tests for judgment seek to codify this.) What the parole judges have to teach us is humbling: We aren't as rational as we imagine and all kinds of extraneous trivia can change our minds—and other peoples'—completely.